Move errno to a pthread_internal_t field.

This change is intended to allow native-bridge to use independent
TLS memory for host and guest environments, while still sharing a
thread-local errno between the two.

Bug: http://b/78026329
Test: bionic unit tests
Change-Id: I838cd321e159add60760bc12a8aa7e9ddc960c33
Merged-In: I838cd321e159add60760bc12a8aa7e9ddc960c33
(cherry picked from commit a9c7c554)